Image sensor device with reflective structure and method for forming the same

ABSTRACT

An image sensor device is provided. The image sensor device includes a semiconductor substrate having a front surface, a back surface opposite to the front surface, at least one light-sensing region close to the front surface, and a first trench surrounding the light-sensing region. The first trench has an inner wall and a bottom surface. The image sensor device includes an insulating layer covering the back surface, the inner wall, and the bottom surface. A thickness of a first upper portion of the insulating layer in the first trench increases in a direction away from the front surface, and the insulating layer has a second trench partially in the first trench. The image sensor device includes a reflective structure filled in the second trench. The reflective structure has a light reflectivity ranging from about 70% to about 100%.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs. Each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs.

In the course of IC evolution, functional density (i.e., the number ofinterconnected devices per chip area) has generally increased whilegeometric size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling-downprocess generally provides benefits by increasing production efficiencyand lowering associated costs.

However, since feature sizes continue to decrease, fabrication processescontinue to become more difficult to perform. Therefore, it is achallenge to form reliable semiconductor devices (e.g., image sensors)at smaller and smaller sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-1I are cross-sectional views of various stages of a process forforming an image sensor device, in accordance with some embodiments.

FIG. 1H-1 is a top view of the image sensor device of FIG. 1H, inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the subject matterprovided. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. It should be understoodthat additional operations can be provided before, during, and after themethod, and some of the operations described can be replaced oreliminated for other embodiments of the method.

FIGS. 1A-1I are cross-sectional views of various stages of a process forforming an image sensor device 200, in accordance with some embodiments.As shown in FIG. 1A, a semiconductor substrate 110 is provided. Thesemiconductor substrate 110 has a front surface 112 and a back surface114 opposite to the front surface 112.

The semiconductor substrate 110 may be a silicon substrate doped with aP-type dopant such as boron, in which case the semiconductor substrate110 is a P-type substrate. Alternatively, the semiconductor substrate110 could be another suitable semiconductor material. For example, thesemiconductor substrate 110 may be a silicon substrate doped with anN-type dopant such as phosphorous or arsenic, in which case thesubstrate is an N-type substrate. The semiconductor substrate 110 mayinclude another elementary semiconductor material such as germanium.

In some embodiments, isolation structures 120 are formed in thesemiconductor substrate 110 to define various light-sensing regions inthe semiconductor substrate 110, and to electrically isolate neighboringdevices (e.g. transistors) from one another. In some embodiments, theisolation features 120 are formed adjacent to or near the front surface112.

In some embodiments, the isolation structures 120 are made of adielectric material, such as silicon oxide, silicon nitride, siliconoxynitride, fluoride-doped silicate glass (FSG), a low-K dielectricmaterial, another suitable material, or a combination thereof. In someembodiments, the isolation structures 120 are formed by using anisolation technology, such as local oxidation of semiconductor (LOCOS),shallow trench isolation (STI), or the like.

In some embodiments, the formation of the isolation structures 120includes patterning the semiconductor substrate 110 by aphotolithography process, etching trenches in the semiconductorsubstrate 110 (for example, by using a dry etching, wet etching, plasmaetching process, or a combination thereof), and filling the trenches(for example, by using a chemical vapor deposition process) with thedielectric material. In some embodiments, the filled trenches may have amulti-layer structure, such as a thermal oxide liner layer and a siliconnitride layer (or a silicon oxide layer) formed thereon.

In some embodiments, the semiconductor substrate 110 is fabricated withfront end processes, in accordance with some embodiments. For example,the semiconductor substrate 110 includes various regions, which mayinclude a pixel region 116R and a non-pixel region 117R (e.g., a logicregion, a periphery region, a bonding pad region, and/or a scribe lineregion).

The pixel region 116R includes pixels each with a light-sensing region116 (also referred to as a radiation-sensing region). The light-sensingregions 116 of the pixels are doped with a doping polarity opposite fromthat of the semiconductor substrate 110. The light-sensing regions 116are formed by one or more implantation processes or diffusion processes.

The light-sensing regions 116 are formed close to (or adjacent to, ornear) the front surface 112 of the semiconductor substrate 110. Thelight-sensing regions 116 are operable to sense incident light (orincident radiation) that enters the pixel region 116R. The incidentlight may be visible light. Alternatively, the incident light may beinfrared (IR), ultraviolet (UV), X-ray, microwave, another suitable typeof light, or a combination thereof.

In some embodiments, the pixel region 116R further includes pinnedlayers, photodiode gates, reset transistors, source followertransistors, and transfer transistors. The transfer transistors areelectrically connected with the light-sensing regions 116 to collect (orpick up) electrons generated by incident light (incident radiation)traveling into the light-sensing regions 116 and to convert theelectrons into voltage signals, in accordance with some embodiments. Forthe sake of simplicity, detailed structures of the above features arenot shown in the figures of the present disclosure.

The non-pixel region 117R includes non-light-sensing regions 117. Thenon-light-sensing regions 117 are doped with a doping polarity oppositefrom or the same as that of the semiconductor substrate 110. Thenon-light-sensing regions 117 are formed by one or more implantationprocesses or diffusion processes. The non-light-sensing regions 117 areformed close to (or adjacent to, or near) the front surface 112 of thesemiconductor substrate 110.

In some embodiments, an interconnection structure 130 is formed over thefront surface 112. The interconnection structure 130 includes a numberof patterned dielectric layers and conductive layers, in accordance withsome embodiments. For example, the interconnection structure 130includes an interlayer dielectric (ILD) layer 132 and a multilayerinterconnection (MLI) structure 134 in the ILD layer 132.

The MLI structure 134 is electrically connected to various dopedfeatures, circuitry, photodiode gates, reset transistors, sourcefollower transistors, and/or transfer transistors formed in and/or overthe semiconductor substrate 110, in accordance with some embodiments.

The MLI structure 134 includes conductive lines 134 a and vias (orcontacts) 134 b connected between the conductive lines 134 a. It shouldbe understood that the conductive lines 134 a and the vias 134 b aremerely exemplary. The actual positioning and configuration of theconductive lines 134 a and the vias 134 b may vary depending on designneeds and manufacturing concerns.

Afterwards, as shown in FIG. 1B, a carrier substrate 140 is bonded withthe interconnection structure 130, in accordance with some embodiments.The carrier substrate 140 includes a silicon substrate, a glasssubstrate, or another suitable substrate. Thereafter, as shown in FIGS.1B and 1C, a thinning process is performed to thin the semiconductorsubstrate 110 from the back surface 114. The thinning process mayinclude a chemical mechanical polishing process.

Afterwards, as shown in FIG. 1D, the semiconductor substrate 110 isflipped over, in accordance with some embodiments. As shown in FIG. 1D,a portion of the semiconductor substrate 110 adjacent to the backsurface 114 over the light-sensing region 116 is removed, in accordancewith some embodiments. The removal of the portion of the semiconductorsubstrate 110 increases the average roughness of the back surface 114over the light-sensing region 116, in accordance with some embodiments.

Therefore, the increase of the average roughness of the back surface 114over the light-sensing region 116 reduces optical reflection from theback surface 114 over the light-sensing region 116 to ensure that mostof the incident light enters the light-sensing regions 116 and issensed, in accordance with some embodiments. Therefore, the quantumefficiency of the light sensing regions 116 is improved by the increaseof the average roughness of the back surface 114 over the light-sensingregion 116, in accordance with some embodiments.

The removal of the portion of the semiconductor substrate 110 formsrecesses R in the semiconductor substrate 110 in the pixel region 116R,in accordance with some embodiments. The removal of the portion of thesemiconductor substrate 110 includes forming a mask layer (not shown)over the back surface 114 in the non-pixel region 117R; performing anetching process; and removing the mask layer, in accordance with someembodiments. The etching process includes a dry etching process or a wetetching process, in accordance with some embodiments.

The recesses R are only formed in the semiconductor substrate 110 in thepixel region 116R and are not formed in the semiconductor substrate 110in the non-pixel region 117R, in accordance with some embodiments.Therefore, the average roughness of the back surface 114 over thelight-sensing region 116 is greater than the average roughness of theback surface 114 over the non-light-sensing region 117, in accordancewith some embodiments.

As shown in FIG. 1D, trenches 118 are formed in the semiconductorsubstrate 110, in accordance with some embodiments. The trenches 118extend from the back surface 114 toward the front surface 112, inaccordance with some embodiments. The trenches 118 are between thelight-sensing regions 116 or between the light-sensing region 116 andthe non-light-sensing region 117, in accordance with some embodiments.

The trenches 118 respectively surround the light-sensing regions 116 andthe non-light-sensing region 117, in accordance with some embodiments.The light-sensing regions 116 are separated from each other by thetrenches 118, in accordance with some embodiments. The light-sensingregions 116 and the non-light-sensing region 117 are separated from eachother by the trenches 118, in accordance with some embodiments.

In some embodiments, the trenches 118 are above the isolation structures120. The trenches 118 are also referred to as deep trenches, inaccordance with some embodiments. In some embodiments, a ratio of adepth D1 of each of the trenches 118 to a thickness T1 of thesemiconductor substrate 110 ranges from about 60% to about 90%.

In some embodiments, the ratio of the depth D1 to the thickness T1 ofthe semiconductor substrate 110 ranges from about 70% to about 80%. Insome embodiments, an aspect ratio D1/W of the depth D1 to a width W ofeach of the trenches 118 ranges from about 6.5 to about 12.5.

As shown in FIG. 1E, a protection layer 150 is conformally formed overthe back surface 114 and bottom surfaces 118 a and inner walls 118 b ofthe trenches 118, in accordance with some embodiments. The protectionlayer 150 is used to induce an electric field in the semiconductorsubstrate 110 so as to neutralize the charges of the defects of thesurface of the semiconductor substrate 110 resulting from the formationof the trenches 118, in accordance with some embodiments. Therefore, theprotection layer 150 may reduce or eliminate the noise of thelight-sensing regions 116 resulting from the charges.

The protection layer 150 conformally and continuously covers the entireback surface 114 over the light-sensing regions 116, the entire bottomsurfaces 118 a, and the entire inner walls 118 b, in accordance withsome embodiments.

The protection layer 150 is made of a high-k material, in accordancewith some embodiments. The high-k material may include hafnium oxide,tantalum pentoxide, zirconium dioxide, aluminum oxide, another suitablematerial, or a combination thereof. The term “high-k material” means amaterial having a dielectric constant greater than the dielectricconstant of silicon dioxide, in accordance with some embodiments.

The protection layer 150 has a first refractive index, and the firstrefractive index is less than a second refractive index of thesemiconductor substrate 110, in accordance with some embodiments.

The dielectric material includes, for example, silicon nitride, siliconoxynitride, another suitable material, or a combination thereof.

As shown in FIG. 1E, an insulating layer 160 is formed over theprotection layer 150, in accordance with some embodiments. In someembodiments, the insulating layer 160 is configured to electricallyisolate structures subsequently formed in the trenches 118 from thesemiconductor substrate 110.

In some embodiments, the insulating layer 160 is also configured topassivate the back surface 114 of the semiconductor substrate 110, thebottom surfaces 118 a, and the inner walls 118 b of the trenches 118. Insome embodiments, the insulating layer 160 is further configured toelectrically isolate the light-sensing regions 116 from one another toreduce electrical crosstalk between the light-sensing regions 116.

The insulating layer 160 includes silicon oxides or another suitableinsulating material. The first refractive index of the protection layer150 is greater than a third refractive index of the insulating layer160, in accordance with some embodiments. The insulating layer 160 isformed by, for example, a chemical vapor deposition process, a physicalvapor deposition process, or an atomic layer deposition process.

As shown in FIG. 1E, an edge G is positioned between the back surface114 and the inner wall 118 b of each of the trenches 118, in accordancewith some embodiments. The deposition rate of the insulating layer 160over the edge G is greater than the deposition rate of the insulatinglayer 160 over the bottom surface 118 a and the inner wall 118 b of eachof the trenches 118, in accordance with some embodiments.

Therefore, voids 162 are formed in the insulating layer 160 in thetrenches 118, in accordance with some embodiments. The voids 162 areclosed voids, which do not communicate with the environment, inaccordance with some embodiments. In some embodiments, each of the voids162 has a lower portion 162 a and an upper portion 162 b. The lowerportion 162 a is in the corresponding trench 118, in accordance withsome embodiments. The upper portion 162 b is outside of thecorresponding trench 118, in accordance with some embodiments.

As shown in FIGS. 1E and 1F, portions of the insulating layer 160 overthe voids 162 are removed to open up the voids 162, in accordance withsome embodiments. The opened voids 162 form trenches 162 c partially inthe corresponding trenches 118, in accordance with some embodiments. Theremoval process includes a dry etching process and/or a wet etchingprocess, in accordance with some embodiments.

As shown in FIG. 1G, a glue layer 170 is conformally formed over theinsulating layer 160, in accordance with some embodiments. The gluelayer 170 is configure to improve the adhesion between the insulatinglayer 160 and a reflective layer subsequently formed on the glue layer170, in accordance with some embodiments.

The glue layer 170 is made of TiN, TaN, or another suitable material.The glue layer 170 is formed using a chemical vapor deposition (CVD)process, a physical vapor deposition (PVD) process, or another suitableprocess. In some other embodiments, the glue layer 170 is not formed.

As shown in FIG. 1G, a reflective layer 180 a is formed on the gluelayer 170 and in the trenches 162 c, in accordance with someembodiments. The trenches 162 c are filled up with the reflective layer180 a (and the glue layer 170), in accordance with some embodiments. Thereflective layer 180 a has a light reflectivity ranging from about 70%to about 100%, in accordance with some embodiments.

The reflective layer 180 a is made of a metal material, an alloymaterial, or another suitable reflective material, in accordance withsome embodiments. The reflective layer 180 a is made of aluminum,silver, copper, titanium, platinum, tungsten, tantalum, alloys thereof,combinations thereof, in accordance with some embodiments. The method offorming the reflective layer 180 a includes a chemical vapor deposition(CVD) process, a physical vapor deposition (PVD) process, or anothersuitable process.

As shown in FIGS. 1G and 1H, the reflective layer 180 a outside of thetrench 162 c is removed, in accordance with some embodiments. Thereflective layer 180 a remaining in the trench 162 c forms a reflectivestructure 180, in accordance with some embodiments.

The reflective structure 180 is configured to reflect incident light toprevent the incident light from traveling between differentlight-sensing regions 116, in accordance with some embodiments.Therefore, the reflective structure 180 reduces crosstalk between thelight-sensing regions 116, in accordance with some embodiments.

As shown in FIG. 1H, an upper portion of the insulating layer 160 underthe removed reflective layer 180 a is removed as well, in accordancewith some embodiments. The removal process includes a chemicalmechanical polishing process, an etching process, or another suitableprocess. In some embodiments, a top surface 182 of the reflectivestructure 180 and a top surface 164 of the insulating layer 160 arecoplanar.

FIG. 1H-1 is a top view of the image sensor device of FIG. 1H, inaccordance with some embodiments. FIG. 1H is a cross-sectional viewillustrating the image sensor device along a sectional line I-I′ in FIG.1H-1, in accordance with some embodiments. As shown in FIGS. 1H and1H-1, the reflective structure 180 continuously surrounds each of thelight-sensing regions 116, in accordance with some embodiments.

The reflective structure 180 continuously surrounds the entirelight-sensing regions 116 or the entire pixel region 116R, in accordancewith some embodiments. The reflective structure 180 has a mesh shape, inaccordance with some embodiments. The reflective structure 180 is acontinuous mesh structure, in accordance with some embodiments.

As shown in FIG. 1I, a planarization layer 190 is formed over the topsurfaces 182 and 162 of the reflective structure 180 and the insulatinglayer 160, in accordance with some embodiments. The planarization layer190 is made of a dielectric material, such as silicon oxide, siliconnitride, silicon oxynitride, another applicable material, or acombination thereof, in accordance with some embodiments. Theplanarization layer 190 is formed using a chemical vapor depositionprocess or a physical vapor deposition process, in accordance with someembodiments.

As shown in FIG. 1I, a color filter structure 210 is formed over theplanarization layer 190, in accordance with some embodiments. The colorfilter structure 210 is configured to filter visible light received bythe light-sensing regions 116 to pass light in a limited spectrum ofwavelengths (e.g., a red wavelength band, a green wavelength band,and/or a blue wavelength band) to the light-sensing regions 116, inaccordance with some embodiments. The color filter structure 210 is madeof a polymer material or another suitable material.

As shown in FIG. 1I, lenses 220 are formed over the color filterstructure 210, in accordance with some embodiments. The lenses 220 areused to direct or focus the incident light. The lenses 220 may include amicrolens array. The lenses 220 may be made of a high transmittancematerial.

For example, the high transmittance material includes a transparentpolymer material (such as polymethylmethacrylate, PMMA), a transparentceramic material (such as glass), another applicable material, or acombination thereof. In this step, an image sensor device 200 issubstantially formed, in accordance with some embodiments.

As shown in FIG. 1I, incident light L passing through the light-sensingregion 116 and arriving at the reflective structure 180 may be reflectedby the reflective structure 180 and thus travel back into thelight-sensing region 116. Therefore, the reflective structure 180 mayreduce optical crosstalk and improve quantum efficiency.

As shown in FIG. 1I, the lenses 220 and the color filter structure 210are only formed in the pixel region 116R, and are not formed in thenon-pixel region 117R, in accordance with some embodiments. In someembodiments, a thickness T2 of an upper portion 160 a of the insulatinglayer 160 in the trench 118 increases in a direction V1 away from thefront surface 112. In some embodiments, a width W2 of an upper portion180 a of the reflective structure 180 decreases in the direction V1. Insome embodiments, a width of a lower portion of the reflective structure180 decreases in a direction toward the front surface 112. Thereflective structure 180 has a substantially oval shape, in accordancewith some embodiments.

In some embodiments, a top portion 180T of the reflective structure 180extends out of the trench 118. The insulating layer 160 is a continuousstructure, in accordance with some embodiments. In some embodiments, afirst average thickness of the insulating layer 160 covering the backsurface 114 over the light-sensing regions 116 is greater than a secondaverage thickness of the insulating layer 160 in the trench 118.

In some embodiments, a thickness T3 of the insulating layer 160 coveringthe back surface 114 over the light-sensing regions 116 is greater thana depth D2 of each of the recesses R. In some embodiments, theinsulating layer 160 covers the entire back surface 114 over thelight-sensing regions 116, the entire bottom surfaces 118 a, and theentire inner walls 118 b.

In some embodiments, the isolation structures 120 are under thereflective structure 180. The reflective structure 180 extends from thetop surface 162 of the insulating layer 160 toward the isolationstructures 120, in accordance with some embodiments. The reflectivestructure 180 and the isolation structures 120 are between thelight-sensing regions 116, in accordance with some embodiments.

In accordance with some embodiments, image sensor devices and methodsfor forming the same are provided. The methods (for forming the imagesensor devices) form a reflective structure in trenches betweenlight-sensing regions in a semiconductor substrate. The reflectivestructure may reflect incident light arriving at the reflectivestructure to prevent the incident light from traveling between thedifferent light-sensing regions. The reflected incident light may bedirected back into the light-sensing region by the reflective structure.Therefore, optical crosstalk is reduced, and quantum efficiency of theimage sensor devices is improved.

In accordance with some embodiments, an image sensor device is provided.The image sensor device includes a semiconductor substrate having afront surface, a back surface opposite to the front surface, at leastone light-sensing region close to the front surface, and a first trenchsurrounding the light-sensing region. The first trench has an inner walland a bottom surface. The image sensor device includes an insulatinglayer covering the back surface, the inner wall, and the bottom surface.A thickness of a first upper portion of the insulating layer in thefirst trench increases in a direction away from the front surface, andthe insulating layer has a second trench partially in the first trench.The image sensor device includes a reflective structure filled in thesecond trench. The reflective structure has a light reflectivity rangingfrom about 70% to about 100%.

In accordance with some embodiments, an image sensor device is provided.The image sensor device includes a semiconductor substrate having afront surface, a back surface opposite to the front surface, at leastone light-sensing region close to the front surface, and a first trenchsurrounding the light-sensing region. The image sensor device includesan insulating layer covering the back surface and an inner wall and abottom surface of the first trench. The insulating layer has a secondtrench partially in the first trench, and a first average roughness ofthe back surface over the light-sensing region is greater than a secondaverage roughness of a top surface of the insulating layer. The imagesensor device includes a reflective structure filled in the secondtrench. The reflective structure has a light reflectivity ranging fromabout 70% to about 100%.

In accordance with some embodiments, a method for forming an imagesensor device is provided. The method includes providing a semiconductorsubstrate including a front surface, a back surface opposite to thefront surface, at least one light-sensing region close to the frontsurface, and a first trench surrounding the light-sensing region. Themethod includes forming an insulating layer over the back surface and inthe first trench. A void is formed in the insulating layer in the firsttrench, and the void is closed. The method includes removing theinsulating layer over the void to open up the void. The opened voidforms a second trench partially in the first trench. The method includesfilling a reflective structure in the second trench. The reflectivestructure has a light reflectivity ranging from about 70% to about 100%.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An image sensor device, comprising: asemiconductor substrate having a front surface, a back surface oppositeto the front surface, and at least one light-sensing region close to thefront surface; an insulating layer covering the back surface andextending into the semiconductor substrate, wherein the insulating layerin the semiconductor substrate surrounds the light-sensing region, and athickness of a first upper portion of the insulating layer in thesemiconductor substrate increases in a direction away from the frontsurface, wherein the insulating layer is a continuous structure, and afirst average thickness of the insulating layer covering the backsurface over the light-sensing region is greater than a second averagethickness of the insulating layer in the semiconductor substrate, areflective layer in the insulating layer in the semiconductor substrate,wherein the reflective layer has a light reflectivity ranging from about70% to about 100%; and wherein a top portion of the reflective layerprotrudes from the semiconductor substrate, and a first top surface ofthe reflective layer and a second top surface of the insulating layerare substantially coplanar.
 2. The image sensor device as claimed inclaim 1, wherein a width of a second upper portion of the reflectivelayer decreases in the direction.
 3. The image sensor device as claimedin claim 1, wherein the reflective layer continuously surrounds theentire light-sensing region.
 4. The image sensor device as claimed inclaim 3, wherein the reflective layer has a mesh shape.
 5. The imagesensor device as claimed in claim 1, further comprising: a protectionlayer between the insulating layer and the semiconductor substrate,wherein the protection layer is made of a high-k material having a firstrefractive index, and the first refractive index is less than a secondrefractive index of the semiconductor substrate.
 6. The image sensordevice as claimed in claim 1, further comprising: an isolation structurein the semiconductor substrate and adjacent to the front surface, andthe isolation structure is under the reflective layer.
 7. The imagesensor device as claimed in claim 1, further comprising: a glue layerbetween the insulating layer and the reflective layer, wherein the gluelayer is in direct contact with the insulating layer and the reflectivelayer.
 8. An image sensor device, comprising: a semiconductor substratehaving a front surface, a back surface opposite to the front surface,and at least one light-sensing region close to the front surface; aninsulating layer covering the back surface and extending into thesemiconductor substrate, wherein the insulating layer in thesemiconductor substrate surrounds the light-sensing region, and a firstaverage roughness of the back surface over the light-sensing region isgreater than a second average roughness of a top surface of theinsulating layer; and a reflective layer in the insulating layer in thesemiconductor substrate, wherein the reflective layer has a lightreflectivity ranging from about 70% to about 100%.
 9. The image sensordevice as claimed in claim 8, wherein the semiconductor substratefurther has a non-light-sensing region, the reflective layer is betweenthe light-sensing region and the non-light-sensing region, the firstaverage roughness of the back surface over the light-sensing region isgreater than a third average roughness of the back surface over thenon-light-sensing region.
 10. The image sensor device as claimed inclaim 8, wherein a width of a first upper portion of the reflectivelayer decreases in a direction away from the front surface.
 11. Theimage sensor device as claimed in claim 10, wherein the insulating layeris a continuous structure, the insulating layer covers the entire backsurface over the light-sensing region, and a thickness of a second upperportion of the insulating layer in the semiconductor substrate increasesin the direction.
 12. The image sensor device as claimed in claim 8,wherein a first average thickness of the insulating layer covering theback surface over the light-sensing region is greater than a secondaverage thickness of the insulating layer in the semiconductorsubstrate.
 13. The image sensor device as claimed in claim 8, furthercomprising: a protection layer between the insulating layer and thesemiconductor substrate, wherein the protection layer is made of ahigh-k material having a first refractive index, and the firstrefractive index is less than a second refractive index of thesemiconductor substrate and greater than a third refractive index of theinsulating layer, and the protection layer conformally and continuouslycovers the back surface and extends into the semiconductor substrate.14. The image sensor device as claimed in claim 8, wherein thereflective layer continuously surrounds the entire light-sensing region.15. An image sensor device, comprising: a semiconductor substrate havinga front surface, a back surface opposite to the front surface, and atleast one light-sensing region extending from the front surface into thesemiconductor substrate; an insulating layer covering the back surfaceand extending into the semiconductor substrate, wherein the insulatinglayer in the semiconductor substrate surrounds the light-sensing region;and a reflective layer in the insulating layer in the semiconductorsubstrate, wherein the reflective layer has a light reflectivity rangingfrom about 70% to about 100%; and a lens over the light-sensing region,the insulating layer, and the reflective layer, wherein a first width ofan upper portion of the reflective layer decreases toward the lens, anda second width of a lower portion of the reflective layer decreasestoward the front surface.
 16. The image sensor device as claimed inclaim 15, further comprising: a glue layer between the insulating layerand the reflective layer.
 17. The image sensor device as claimed inclaim 15, wherein a first average roughness of the back surface over thelight-sensing region is greater than a second average roughness of a topsurface of the insulating layer.
 18. The image sensor device as claimedin claim 17, further comprising: a protection layer between theinsulating layer and the semiconductor substrate, wherein the protectionlayer conformally covers the back surface.
 19. The image sensor deviceas claimed in claim 18, wherein the protection layer is made of a high-kmaterial having a first refractive index, and the first refractive indexis less than a second refractive index of the semiconductor substrate.